Flow modification in body lumens

ABSTRACT

The devices and methods described herein include an implantable body lumen fluid flow modulator including an upstream flow accelerator separated by a gap from a downstream flow decelerator. The gap is a pathway to entrain additional fluid from a branch lumen(s) into the fluid stream flowing from the upstream flow accelerator to the downstream flow decelerator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication Ser. No. 62/537,067, filed Jul. 26, 2017, and U.S.Provisional Application Ser. No. 62/514,020, filed Jun. 2, 2017, theentire contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to devices and methods foraltering flow in body lumens, such as devices and methods for creatingpressure differences and/or entrainment of fluid at lumens that branchoff from other lumens for enhancing or modifying fluid flow to treatdifferent disorders or diseases.

BACKGROUND OF THE INVENTION

Heart failure is the physiological state in which cardiac output isinsufficient to meet the needs of the body and the lungs. Patientssuffering from any of a number of forms of heart failure are prone toincreased fluid in the body. Congestive heart failure (CHF) occurs whencardiac output is relatively low and the body becomes congested withfluid. There are many possible underlying causes of CHF, includingmyocardial infarction, coronary artery disease, valvular disease, andmyocarditis. Chronic heart failure is associated with neurohormonalactivation and alterations in autonomic control. Although thesecompensatory neurohormonal mechanisms provide valuable support for theheart under normal physiological circumstances, they also have afundamental role in the development and subsequent progression of CHF.For example, one of the body's main compensatory mechanisms for reducedblood flow in CHF is to increase the amount of salt and water retainedby the kidneys. Retaining salt and water, instead of excreting it intothe urine, increases the volume of blood in the bloodstream and helps tomaintain blood pressure. However, the larger volume of blood alsostretches the heart muscle, enlarging the heart chambers, particularlythe ventricles. At a certain amount of stretching, the heart'scontractions become weakened, and the heart failure worsens. Anothercompensatory mechanism is vasoconstriction of the arterial system. Thismechanism, like salt and water retention, raises the blood pressure tohelp maintain adequate perfusion.

Glomerular filtration rate (GFR), the rate at which the kidney filtersblood, is commonly used to quantify kidney function and, consequently,the extent of kidney disease in a patient. Individuals with normalkidney function exhibit a GFR of at least 90 mL/min with no evidence ofkidney damage. The progression of kidney disease is indicated bydeclining GFR, wherein a GFR below 15 mL/min generally indicates thatthe patient has end stage renal disease (ESRD), which is the completefailure of the kidney to remove wastes or concentrate urine.

Cardiovascular problems, such as but not limited to, inadequate bloodflow or chronic hypertension, may lead to fluid retention in thekidneys, chronic kidney disease, lowered GFR, renal failure or evenESRD. For example, hypertension is considered the second most prevalentcause for kidney failure (after diabetes). It is been estimated thathypertension causes nephrotic damage and lowers GFR.

Therefore, it would be desirable to provide apparatus and methods toimprove blood flow to prevent disease, improve body functionality,and/or treat conditions that would benefit from modified body fluidflow. For example, it would be desirable to treat heart failure, treathypertension, prevent kidney disease, improve kidney functionality,and/or prevent blood clots from flowing through vasculature to sensitiveportions of the body, such as the brain, in order to prevent strokes.

SUMMARY OF THE INVENTION

The present invention seeks to provide devices and methods for alteringflow in body lumens, as is described more in detail hereinbelow. Forexample, devices and methods are provided for creating pressuredifferences and/or fluid entrainment at lumens that branch off fromother lumens for enhancing or modifying fluid flow to treat differentdisorders or diseases.

The devices and methods of the present invention have many applications.For example, the device may be used to reduce pressure and improve flow,thereby improving flow in stenotic body lumens. It also may be used inthe aortic arch to reduce peak systolic pressure in the brain or divertemboli to other portions of the body (e.g., the legs) and thereby reducethe risk of stroke. The device further may be installed in a bifurcation(e.g., in the brachiocephalic vessels) to reduce peak pressure gradientsor to divert emboli with very little energy loss.

The devices and methods of the present invention have particularapplication in treating blood flow to and from the kidneys. Inaccordance with one embodiment, the device is configured to be installednear one of the renal arteries or in the inferior vena cava near thebranch off to the renal veins or in one of the renal veins.

When installed in the inferior vena cava or in the renal vein, thedevice can create (due to the Bernoulli effect or other factors) aregion in the inferior vena cava or in the renal vein which hasincreased blood velocity and reduced pressure. In this manner, blood maybe drawn from the kidneys to the renal veins and then to the inferiorvena cava, thereby improving kidney functionality and reducing necroticdamage to the kidneys.

When installed in or near the renal vein, the devices of the presentinvention may improve renal function by improving net filtrationpressure, which is glomerular capillary blood pressure—(plasma-colloidosmotic pressure+Bowman's capsule hydrostatic pressure), e.g., 55 mmHg—(30 mm Hg+15 mm Hg)=10 mm Hg. The devices and methods of the presentinvention thus provide an improvement over existing therapies, such asdiuretics (although the invention can be used in addition to diuretics),angiotensin-converting enzyme inhibitors (ACEIs), and angiotensinreceptor blockers (ARBs), which can have deleterious effects on kidneyfunction. When used in conjunction with current modes of treatment suchas diuretics, the devices and methods of the present invention areexpected to improve the response for diuretics and reduce the dosageneeded to obtain therapeutic benefit of such previously known therapies,without the disadvantages of these existing therapies.

The devices and methods of the present invention may be used to divertflow from the kidneys to the inferior vena cava with little energy loss.For example, with a small energy loss due to pressure drop and otherfluid factors, a significantly greater increase in blood flow may beachieved. This diversion of flow from the kidneys with little energyloss to increase blood flow is expected to treat conditions such asheart failure and/or hypertension.

It is noted that there is a significant difference between use of anupstream nozzle with no downstream flow decelerator, such as a diffuser.If only an upstream nozzle is placed in the flow path, there issignificant energy loss downstream of the nozzle due to the suddenexpansion of flow. However, by using a downstream flow decelerator, suchas a diffuser, the energy loss is significantly reduced. This leads toanother advantage: since the energy loss is significantly reduced, theadditional flow that flows into the gap is efficiently added to the flowfrom the upstream flow accelerator.

In addition, the present invention is expected to provide optimalstructure for an upstream flow accelerator when used together with adownstream flow decelerator. For example, the distance between theoutlet of the upstream flow accelerator and the inlet of the downstreamflow decelerator should be less than a predetermined length to reducepressure at the gap between the outlet and the inlet.

When installed in the renal artery, the device can reduce pressureapplied to the kidneys. Without being limited by any theory, high bloodpressure can cause damage to the blood vessels and filters in thekidney, making removal of waste from the body difficult. By reducing thepressure in the renal artery, the filtration rate improves. Althoughthere may be a reduction in the perfusion pressure, the filtration ratewill increase because the overall kidney function is more efficient.

It is noted that the fluid flow modulator of the present invention maymodulate fluid flow without any input from an external energy source,such as a fan, motor, and the like and without any moving parts. Thestructure of the device of the invention transfers energy from one lumenflow to another different lumen flow with minimal flow energy losses.

In accordance with one aspect of the present invention, an implantabledevice is provided for altering fluid flow through a body lumen (e.g.,the inferior vena cava) that is coupled to a branch lumen(s) (e.g., arenal vein(s)). The implantable device includes a flow modulatorconfigured to be implanted within the body lumen. The flow modulatorpreferably has an upstream component separated by a gap from adownstream component. The flow modulator may be formed as a single unit(e.g., from a single frame) or multiple units. The upstream componenthas an inlet, an outlet, and a cross-sectional flow area that preferablyconverges from the inlet towards the outlet. The downstream componenthas an entry, an exit, and a cross-sectional flow area that preferablydiverges from the entry towards the exit. The gap defines a pathway thatcommunicates with the branch lumen,

The flow modulator preferably accelerates a fluid stream passing throughthe upstream component towards the downstream component to generate alow pressure region in the vicinity of the gap and to entrain additionalfluid into the fluid stream as the fluid stream passes into the entry ofthe downstream component.

The outlet of the upstream component is preferably spaced apart from theentry of the downstream component a suitable distance for increasingflow within the branch lumen(s) while minimizing pressure loss. Forexample, the distance from the outlet to the entry may be less than 15mm.

In accordance with one aspect, the cross-sectional flow area at theoutlet of the upstream component is less than the cross-sectional flowarea at the entry of the downstream component. The outlet of theupstream component may be positioned downstream from where the branchlumen first intersects with the body lumen. The gap may begin downstreamfrom where the branch lumen first intersects with the body lumen. Theupstream component and the downstream component may share a common,collinear flow axis with the body lumen's flow axis. The outlet of theupstream component may be positioned downstream from the entry of thedownstream component.

In one example, the upstream component is coupled to the downstreamcomponent via a fluid flow structure that defines the gap. The upstreamcomponent, the downstream component, and the fluid flow structure may beformed from a single frame. The fluid flow structure may extend outwardfrom the upstream component and from the downstream component such thatthe fluid flow structure contacts an inner wall of the body lumen. Ajunction between the fluid flow structure and the upstream componentand/or the downstream component may have a curved shape such as anS-curve shape.

In accordance with one aspect, the downstream component's length isgreater than the upstream component's length. The upstream component'saverage angle of convergence may be greater than the downstreamcomponent's average angle of divergence. The upstream component mayinclude a nozzle that accelerates the fluid stream passing through theupstream component and the downstream component may include a diffuserthat decelerates the fluid stream having the entrained additional fluidpassing through the downstream component.

The flow modulator may be formed from a metal frame. The metal frame maybe coated with a biocompatible material at the upstream component and atthe downstream component. In one example, an uncoated portion of themetal frame between the upstream and downstream components defines thegap that allows fluid from the branch lumen(s) to entrain with the fluidstream flowing through the flow modulator.

In accordance with another aspect, a method for altering fluid flowthrough a body lumen coupled to a branch lumen is provided. The methodmay include implanting a flow modulator within a body lumen, the flowmodulator including an upstream component separated by a gap from adownstream component, the upstream component being implanted in a firstbody lumen portion and having an inlet, an outlet, and a cross-sectionalflow area that converges from the inlet towards the outlet, thedownstream component being implanted in a second body lumen portion andhaving an entry, an exit, and a cross-sectional flow area that divergesfrom the entry towards the exit. The gap may be positioned where thebranch lumen intersects with the body lumen and the outlet may bepositioned downstream from where the branch lumen first intersects withthe body lumen. The method may include accelerating a fluid streampassing through the upstream component towards the downstream componentto generate a low pressure region in the vicinity of the gap and toentrain additional fluid into the fluid stream as the fluid streampasses into the entry of the downstream component.

Implanting the flow modulator within the body lumen may includeimplanting the upstream component in an inferior vena cava such that theinlet is upstream from a branch off to a renal vein(s) and thedownstream component in the inferior vena cava such that the exit isdownstream from the branch off to the renal vein(s), wherein the gap isat the branch to the renal vein(s), thereby drawing blood from the renalvein(s) to the inferior vena cava and improving kidney functionality.Drawing the blood from the renal vein(s) to the inferior vena cava toimprove kidney functionality may further reduce excess fluid to treatheart failure.

The flow modulator may modulate fluid flow without any input from anexternal energy source. The flow modulator may modulate fluid flowwithout any moving parts.

There is thus provided in accordance with an embodiment of the presentinvention a system including a body-lumen fluid flow modulator includingan upstream flow accelerator separated by a gap from a downstream flowdecelerator, wherein the gap is a pathway to entrain additional fluidwith fluid flowing from the upstream flow accelerator, to the downstreamflow decelerator.

The gap may be located in a fluid flow structure that defines boundariesfor the pathway to entrain the additional fluid to flow to thedownstream flow decelerator. The upstream flow accelerator may have aflow cross-section that converges in a downstream direction. Thedownstream flow decelerator may have a flow cross-section that divergesin a downstream direction. The fluid flow structure may include one ormore conduits that are not collinear with a direction of flow from theupstream flow accelerator to the downstream flow decelerator. Theupstream flow accelerator and the downstream flow decelerator may sharea common, collinear flow axis. The fluid flow structure may or may notconnect the upstream flow accelerator to the downstream flowdecelerator. The fluid flow structure may diverge outwards in adirection away from a central axis of the fluid flow structure. Ajunction between the fluid flow structure and at least one of theupstream flow accelerator and the downstream flow decelerator may becurved.

There is provided in accordance with an embodiment of the presentinvention a method for altering fluid flow through a body lumenincluding installing a fluid flow modulator in a body, the fluid flowmodulator including an upstream flow accelerator separated by a gap froma downstream flow decelerator, the upstream flow accelerator beinginstalled in a first body lumen portion, the downstream flow deceleratorbeing installed in a second body lumen portion and the gap beingpositioned at a branch lumen tilted with respect to the first and secondbody lumen portions, wherein when fluid flows from the upstream flowaccelerator to the downstream flow decelerator, additional fluid isentrained into the gap and is added to the fluid flowing from theupstream flow accelerator to the downstream flow decelerator.

In one method, the fluid flow modulator is installed near renal arteriesto improve renal function by reducing renal perfusion pressure.

In one method, the fluid flow modulator is installed near a bifurcationto divert emboli from the bifurcation.

In one method, the fluid flow modulator is installed in an aortic archto reduce peak systolic pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic view of a fluid flow modulator, constructed andoperative in accordance with a non-limiting embodiment of the presentinvention;

FIG. 2 is a side-sectional view of a fluid flow modulator, constructedand operative in accordance with another non-limiting embodiment of thepresent invention;

FIGS. 3A-19 are schematic views of different fluid flow modulators ofthe invention, some of which are shown installed in various body lumens,in accordance with non-limiting embodiments of the present invention;

FIGS. 20 and 21 are side views of illustrative flow acceleratorsconstructed in accordance with the principles of the present invention;

FIG. 22 is a schematic view of a fluid flow modulator, in accordancewith another non-limiting embodiment of the present invention, andincluding a pump (either downstream or upstream);

FIG. 23 is a schematic view of a fluid flow modulator installed in ananeurysm, in accordance with a non-limiting embodiment of the presentinvention;

FIG. 24 is a schematic view of a fluid flow modulator, in accordancewith another non-limiting embodiment of the present invention, in whichan outlet nozzle of an upstream flow accelerator enters a mouth portionof a downstream flow decelerator;

FIG. 25 is a schematic view of a fluid flow modulator, in accordancewith another non-limiting embodiment of the present invention, with anupstream flow accelerator that has a portion which is not in-line with adownstream flow decelerator, but is instead tilted relative thereto andwhich may be installed in a branch lumen;

FIG. 26 is a schematic view of a lumen support member used with a fluidflow modulator, in accordance with another non-limiting embodiment ofthe present invention;

FIG. 27 is a schematic view of a fluid flow modulator, in accordancewith another non-limiting embodiment of the present invention, in whichthe upstream flow accelerator and/or downstream flow decelerator may notseal against the inner contour of the body lumen;

FIG. 28 is a schematic view of an asymmetric transition between theupstream flow accelerator and the downstream flow decelerator, inaccordance with another non-limiting embodiment of the presentinvention;

FIGS. 29A and 29B are views of an upstream flow accelerator or adownstream flow decelerator, whose shape is changeable in accordancewith another non-limiting embodiment of the present invention, whereinFIG. 29B is a sectional view taken along lines B-B in FIG. 29A;

FIGS. 30-34 are schematic views of fluid flow modulators, in accordancewith non-limiting embodiments of the present invention, shown indelivery and retrieval-type configurations; and

FIGS. 35-37E are the results from a bench top test used for determiningpreferred configurations for flow modulators constructed in accordancewith the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Provided herein are devices and methods for altering flow in bodylumens. For example, the devices and methods may be provided forcreating pressure differences and/or fluid entrainment at lumens thatbranch off from other lumens for enhancing or modifying fluid flow totreat different disorders or diseases.

Reference is now made to FIG. 1, which illustrates flow modulator 10,constructed and operative in accordance with a non-limiting embodimentof the present invention.

Flow modulator 10 includes upstream component 12 separated by gap 14from downstream component 16. Gap 14 is a pathway to divert or entrainadditional fluid into a stream of fluid flowing from upstream component12 to downstream component 14. As will be explained below, upstreamcomponent 12 and downstream component 16 create a lower pressure regionin the vicinity of gap 14, which preferably entrains fluid into thestream of fluid flowing across gap 14. Fluid entrainment is fluidtransport by shear-induced turbulent flux. In accordance with theprinciples of the invention, such entrainment may help transport bloodor other body fluids to or from a region so as to promote betterfunctionality of an organ (e.g., from the renal vein(s) to the inferiorvena cava to promote better functionality of the kidney(s), therebytreating disorders and/or diseases such as heart failure).

Upstream component 12 has inlet 13 and outlet 15 and preferably has across-sectional flow area that converges in a downstream direction(indicated by arrow 17) along part or all of the length of upstreamcomponent 12, such as but not limited to, a nozzle. In this manner,upstream component 12 acts to accelerate flow of fluid through upstreamcomponent 12. Downstream component 16 has entry 21 and exit 23 andpreferably has a cross-sectional flow area that diverges in a downstreamdirection along part or all of the length of downstream component 16,such as but not limited to, a diffuser. In this manner, downstreamcomponent 16 acts to decelerate flow of fluid through downstreamcomponent 16. The distance between outlet 15 and entry 21 is selected togenerate a low pressure region in the vicinity of gap 14 whileminimizing pressure loss and reducing resistance to fluid flow at thebranch lumen(s), e.g., renal flow. For example, as explained in the databelow, a distance too great will create a significant pressure loss thatactually sends flow in the wrong direction in a branched lumen.Applicant has discovered that using a maximum distance between outlet 15and entry 21 (e.g., less than 25 mm and more preferably less than 15 mmwhen used at the renal veins) will improve flow rates in the branchedvessel(s) with relatively low pressure loss. Gap 14 also permits flowmodulator 10 to entrain additional fluid into the fluid stream as thefluid stream passes into entry 21 of downstream component 16.

PCT Patent Applications WO 2016/128983 and WO 2018/029688, as well asU.S. Provisional Application Nos. 62/586,258 and 62/630,406, describeseveral converging and diverging structures which may be utilized forcreating flow modulator 10 in accordance with the principles describedherein, and the disclosures of each of which are incorporated herein byreference in their entireties. Other non-limiting converging anddiverging structures are shown in FIGS. 2-34. The invention may becarried out with different kinds of converging and diverging structures,such as but not limited to, Stratford ramp nozzles (e.g., in which flowthrough the nozzle is on the verge of separation, which gives thediffuser the best length to efficiency ratio), de Laval nozzles (e.g.,asymmetric hourglass shape), variable cross-sectional area nozzles andventuris, ramped nozzles and venturis, and many others. The central axisof the diverging portion may be in-line with or offset from the centralaxis of the converging portion.

Gap 14 may be located in fluid flow structure 18 which definesboundaries for the pathway to divert or entrain the additional fluid toflow to downstream component 16. Fluid flow structure 18 may include oneor more conduits that are not collinear with a direction of flow(indicated by arrow 17) from upstream component 12 to downstreamcomponent 16. For example, the conduits of fluid flow structure 18 maybe perpendicular to direction of flow or may be tilted at an angle,e.g., 30° angle, 45° angle or any other suitable configuration.

In the embodiment of FIG. 1, upstream component 12 and downstreamcomponent 16 share a common, collinear flow axis 19. However, theinvention is not limited to this construction and upstream component 12may be tilted with respect to downstream component 16. Upstreamcomponent 12 and downstream component 16 may lie along a continuouscurved path.

Fluid flow structure 18 may or may not connect upstream component 12 todownstream component 16. For example, if fluid flow structure 18 employsconduits, then fluid flow structure 18 preferably connects upstreamcomponent 12 to downstream component 16. However, fluid flow structure18 as shown in FIG. 1 may not be conduits, but instead two walls thatare not connected to each other. In such an example, fluid flowstructure 18 does not connect upstream component 12 to downstreamcomponent 16.

Upstream component 12, downstream component 16, and fluid flow structure18 may be constructed as grafts, stents (coated or uncoated), stentgrafts (coated or uncoated), catheters and the like, with knownmedically safe materials, such as stainless steel or nitinol. The outercontours of any of upstream component 12, downstream component 16, andfluid flow structure 18 may be sealed against the inner walls of thebody lumen (such as by being expanded thereagainst), or alternativelymay not be sealed, depending on the particular application.

Flow modulator 10 is sized and shaped to be implanted in a body lumen.Flow modulator 10 may be compressible for delivery (e.g., percutaneousdelivery within a delivery sheath) and expandable upon deployment (e.g.,self-expanding upon exposure from the end of the delivery sheath orballoon expandable). Flow modulator 10 may be inserted into the bodylumen in an antegrade or retrograde manner and may be removed antegradeor retrograde. Flow modulator may be used as an acute device to beremoved after few hours/days or a chronic permanent device or a devicethat can be retrieved after long-term implantation. When used as anacute device, flow modulator 10 may remain coupled to adelivery/retrieval device, e.g., sheath and/or wire/shaft, throughoutthe short-term implantation for ease of device delivery and retrieval.Flow modulator 10 may be compressible within a body lumen to allowwashing of any stagnant flow zones created adjacent to flow modulator10. For example, flow modulator 10 may be partially or fully reduced indiameter within the body lumen to allow blood flow through a stagnantflow zone. Preferably, upon expansion, flow modulator 10 is sized tocontact the inner wall of the body lumen to anchor flow modulator 10 inplace. Flow modulator 10 preferably is formed from one or more framesand may be coated with one or more biocompatible materials. For example,the frame(s) may be formed of a metal (e.g., shape memory metal) oralloy or a combination thereof (e.g., a stent made of stainless steel ornitinol or cobalt chromium). For some applications, the frame(s) may beformed in the manner of a braided stent. In the case of more than oneframe, the frames may be joined together by a suitable technique such aswelding. For example, upstream component 12 and downstream component 16may be formed from a common frame or two frames that may be joined priorto implantation. Flow modulator 10 may be at least partially coated witha biocompatible, covering material (although they may be used as baremetal, uncoated stents as well). The biocompatible material may be afabric and/or polymer such as expanded polytetrafluoroethylene (ePTFE),woven, knitted, and/or braided polyester, polyurethane, DACRON(polyethylene terephthalate), silicone, polycarbonate urethane, orpericardial tissue from an equine, bovine, or porcine source. Thebiocompatible coating may impede or block fluid flow where applied tothe frame. The order of the joining and coating processes may be joiningbefore coating or coating before joining. The biocompatible material maybe coupled to the frame(s) via stitching, spray coating, encapsulation,electrospinning, dip molding, and/or a different technique.

In a preferred embodiment, biocompatible material is fluid impermeable.However, for some applications, the surfaces need not be impermeable,but have a permeability that is sufficiently low as to substantiallyprevent any blood from flowing through the longitudinal portion of thebody lumen, via any flow path other than through the flow channeldefined by the inner surfaces of flow modulator 10. For someapplications, each of the surfaces has permeability per unit length ofless than 0.25 micrometers (i.e., between 0 and 0.25 micrometers), wherethe permeability per unit length is defined based upon the followingequation, which is based upon Darcy's Law: k/Δx=Vμ/4p, where k ispermeability, Δx is length (in meters), V is average velocity (in metersper second), μ is fluid viscosity (measured in Pascal-seconds), and ΔPis the pressure differential measured in Pascals).

Although the invention is not bound by any theory, a simplifiedengineering explanation is now provided to help understand how upstreamcomponent 12 and downstream component 16 operate to create reducedpressure at gap 14.

The Bernoulli equation governs the relationship between fluid velocityand pressure (neglecting the height difference):

P ₁+½·ρ·V ₁ ² =P ₂+½·ρ·V ₂ ² +E _(loss)

-   -   P=pressure    -   ρ=density    -   V=velocity    -   1=conditions at the inlet (upstream component 12)    -   2=conditions at gap 14    -   Mass conservation (same flow rate):

V ₁ ·A ₁ =V ₂ ·A ₂

-   -   A=Flow cross section    -   E_(loss)=Energy loss

For example, if flow modulator 10 is installed near the kidneys withupstream component 12 in the inferior vena cava, then V₁ and A₁ are therenal velocity and flow area, respectively, at the inferior vena cava.

The flow velocity at the gap (V₂) is designed to achieve the desiredpressure reduction. For example, without limitation, with a 0.5 meterper second velocity and 3 times area ratio, a suction of ˜6-8 mmHg canbe achieved. In the case of installation near the kidney, this canimprove renal function by improving renal perfusion pressure.

In another example, flow modulator 10 can be installed near abifurcation to divert emboli from the bifurcation. In another example,flow modulator 10 can be installed in the aortic arch to reduce peaksystolic pressure.

Reference is now made to FIG. 2, which illustrates another version offlow modulator 10, with like elements being designated by like numerals.In this version, fluid flow structure 18 includes central portion 20,which may be cylindrical, that connects upstream component 12 todownstream component 16. Fluid flow structure 18 extends outward fromoutlet 15 of upstream component 12 and from entry 21 of downstreamcomponent 16 such that fluid flow structure 18 is sized to contact aninner wall of the body lumen. Central portion 20 may be formed with oneor more apertures 22 to define gap 14 for fluidly communicating withbranch lumens such that additional fluid from the branch lumen or lumensflows into gap 14 and is added to the fluid flowing from upstreamcomponent 12 to downstream component 16.

It is noted that junction 24 between fluid flow structure 18 andupstream component 12 and/or downstream component 16 is curved. This mayhelp streamline the flow, and prevent creation of local turbulences oreddy currents that may adversely affect the pressure or flowcharacteristics. It is also noted that fluid flow structure 18 maydiverge outwards (at numeral 26) in a direction away from central axis28 of fluid flow structure 18. This diversion may be used to createdifferent flow affects, depending on the application. The diversion alsoenables moving upstream component 12 and downstream component 16 closerto each other. For example, junction 24 between fluid flow structure 18and upstream and downstream components 12 and 16 may be S-shaped to moveoutlet 15 closer to entry 21 to minimize the distance between thoseparts of fluid modulator 10.

As best shown in FIG. 2, fluid modulator 10 is formed from frame 25 andcoated with biocompatible material 27. The potential materials for frame25 and biocompatible material 27 are described above. In FIG. 2, fluidmodulator 10 is formed of one frame that defines upstream component 12,gap 14, and downstream component 16. Upstream component 12 is coatedwith biocompatible material 27 to define the fluid flow channel throughupstream component 12 such that fluid flowing through a body lumenenters inlet 13, accelerates through the converging portion of upstreamcomponent 12, and exits out outlet 15 into the portion of fluidmodulator 10 having gap 14. At gap 14, there is a low pressure regionformed by the shapes of upstream component 12 and downstream component16. Also, additional fluid from the branch lumen(s) at gap 14 isentrained into the fluid stream passing from outlet 15 to entry 21.Downstream component 16 also is coated with biocompatible material 27 todefine the fluid flow channel through downstream component 16 such thatthe fluid stream from outlet 12 together with the additional fluidpassing through gap 14 enter entry 21, decelerate through the divergingportion of downstream component 16, and exit out exit 23 back into thebody lumen. In this example, gap 14 is created by an uncoated portion offrame 25.

Upstream component 12 may have fixation area 29 sized for anchoringupstream component 12 within the body lumen. Fixation area 29 is sizedto contact the inner wall of the body lumen and preferably has adiameter the size of, or slightly larger than, the diameter of the bodylumen. Fixation area 29 may have a constant diameter for a lengthsuitable for anchoring upstream component 12 in the body lumen.Similarly, downstream component 16 may have fixation area 30 sized foranchoring downstream component 16 within another portion of the bodylumen. Fixation area 30 is sized to contact the inner wall of the otherportion of the body lumen and preferably has a diameter the size of, orslightly larger than, the diameter of that portion of the body lumen.Fixation area 30 may have a constant diameter for a length suitable foranchoring downstream component 16 in the body lumen. Preferably fixationareas 29 and 30 are configured to seal fluid modulator 10 within thebody lumen so that fluid only flows into the fluid channels created byfluid modulator 10 and does not flow around fixation area 29 or fixationarea 30. In FIG. 2, fluid flow structure 18 has the same diameter asfixation areas 29 and 30, which may enhance anchoring immediatelyproximal and distal to the branch lumen(s) while positioning gap 14 atthe intersection between the body lumen and the branch lumen(s). In thismanner, fluid flow structure 18 forms one or more additional fixationareas (illustratively, two additional fixation areas) between fixationareas 29 and 30. As shown, the portions of fluid flow structure 18coated with biocompatible material 27 (on opposing sides of uncoatedframe 25 that defines gap 14) act as fixation/sealing areas. Fluidflowing in the body lumen may be trapped between the outer surface ofupstream component 12 and the body lumen wall between fixation area 29and the upstream portion of fluid flow structure 18. In addition, oralternatively, fluid flowing in the body lumen may be trapped betweenthe outer surface of downstream component 16 and the body lumen wallbetween fixation area 30 and the downstream portion of fluid flowstructure 18.

Referring now to FIG. 3A, an exemplary flow modulator is shown withsymbols depicting dimensions of flow modulator 10 in accordance with apreferred embodiment. The dimensions provided with respect to FIG. 3 arefor an embodiment where flow modulator 10 is configured for implantationin the inferior vena cava such that inlet 13 of upstream component 12 isupstream from a branch off to a renal vein(s) and downstream component16 is in the inferior vena cava such that exit 23 is downstream from thebranch off to the renal vein(s) and gap 14 is at the branch to the renalvein(s). d1 is the diameter of outlet 15 of upstream component 12. d1 isselected to create a jet velocity for a given device resistance. In theexample of chronic cases, d1 may be in a range from 4-8 mm. In acutecases, d1 preferably is in a range from 3-7 mm. d2 is the diameter ofinlet 13 in the deployed, expanded state and may be in a range from12-40 mm. 11 is the length of fixation area 29 and may be in a rangefrom 5-30 mm. 12 is the overall length of upstream component 12 and maybe in a range from 15-60 mm. x is the distance from outlet 15 ofupstream component 12 to entry 21 of downstream component. For x, aminimum distance from outlet 15 to entry 21 will provide betterperformance for downstream component 16, but the renal flow will belower because there is a greater resistance to flow from the renalvein(s) to downstream component 16. Thus, distance x preferably isselected (e.g., in a range from −5-25 mm) to provide improved renal flowrate with minimal pressure loss.

As illustrated below, distance x may be negative as outlet 15 ofupstream component 12 may be positioned downstream from entry 21 ofdownstream component 16. a is the distance from outlet 15 of upstreamcomponent 12 to the center line of the branched lumen, e.g., the rightrenal vein, and may be in a range from −25-25 mm. L1 is the length offixation area 30 and may be in a range from 5-30 mm. L2 is the overalllength of downstream component 16. L2 is preferably greater than 12because a diverging shape creates a much higher pressure loss than aconverging shape. The ratio of L2:12 may be from 1:1 to 3:1. D1 is thediameter at entry 21 of downstream component 16 and is preferably largerthan d1. Thus, the cross-sectional flow area at outlet 15 of upstreamcomponent 12 is less than the cross-sectional flow area at entry 21 ofdownstream component 16. D1 is selected to receive all the fluid jettedfrom outlet 15. The ratio of D1:d1 may be from 1:1 to 2:1. In addition,D1 should be greater for larger distances x to ensure receipt of thefluid jetted from upstream component 12. D2 is the diameter of exit 23in the deployed, expanded state and may be in a range from 12-40 mm. αis the average angle of divergence in downstream component 16 and may bein a range from 5-30 degrees. Preferably, the angle of divergence indownstream component 16 is less than the angle of convergence inupstream component 12, as illustrated. Such structure is expected toprevent pressure loss. In addition, downstream component 16 should haveslow change in area adjacent to entry 21 (closer to the renal vein)—anyadditional pressure loss will reduce the inferior vena cava flow rateand thus will reduce the effectiveness of the device. The angle ofdivergence in downstream component 16 may be constant or may changealong the length of downstream component 16. When the angle ofdivergence changes along the length (as shown in FIG. 2, for example)the angle of divergence is preferably smallest (e.g., in a range from5-30 degrees) adjacent to entry 21. A slow change in the cross-sectionalflow area adjacent to entry 21 is preferable because the fluid velocitydecreases as the cross-sectional flow area increases, hence the pressureloss. Accordingly, the angle of divergence is smallest at entry 21 wherethe fluid flow is at maximum velocity within downstream component 16.

Fluid modulator 10 of FIG. 3A may be formed from one frame that definesupstream component 12, gap 14, and downstream component 16. In thisexample, upstream component 12 and downstream component 16 are eachcoated with a biocompatible material while gap 14 is created by anuncoated portion of the frame.

FIG. 3B shows flow modulator 10 of FIG. 3A implanted in the inferiorvena cava at the renal veins. Upstream component 12 is in the inferiorvena cava such that inlet 13 is upstream from a branch off to the leftand right renal veins and downstream component 16 is in the inferiorvena cava such that exit 23 is downstream from the branch off to therenal veins. While the right and left renal veins are usually atdifferent heights along the inferior vena cava, gap 14 is generallypositioned in the vicinity of the branches to the renal veins (or otherbranch lumens when used for other indications). For example, gap 14 maybegin downstream from where the renal veins first intersect with theinferior vena cava, as illustrated. In addition, gap 14 may be entirelydisposed within the intersection between the renal veins and theinferior vena cava, as illustrated. Outlet 15 of upstream component 12may be positioned downstream from where the renal veins first intersectwith the inferior vena cava, as shown. Accordingly, blood only entersfluid modulator 10 at inlet 13 and gap 14, which is downstream fromwhere the branch lumen first intersects the main lumen. Entry 21 ofdownstream component 16 may be positioned upstream from where theintersection of the renal veins and the inferior vena cava ends, asshown. Flow modulator 10 creates reduced pressure at gap 14 andincreases blood flow velocity to gap 14. Entrainment may also helptransport blood to gap 14 from the kidneys. In this manner, theinvention may draw blood from the kidneys to the renal veins and then tothe inferior vena cava, thereby improving kidney functionality, reducingnecrotic damage to the kidneys, and/or treating heart failure.

Reference is now made to FIGS. 4-29B, which illustrate different flowmodulators of the invention, in accordance with non-limiting embodimentsof the present invention. Once again, like elements are designated bylike numerals.

In FIG. 4, flow modulator 10 is constructed similarly to fluid modulatorof FIG. 3A although flow modulator 10 of FIG. 4 includes one or moreopenings 31 to prevent stagnant flow zones. Fluid entering fluidmodulator 10 flows out of openings 31 and into the body lumen. Openings31 act as flashing flow channels for fluid and may encompass the entirecircumference of fluid modulator 10 or be ports. Upstream component 12or downstream component 16 or both (as illustrated) may include one ormore openings 31. As shown, openings 31 may be on the converging portionof upstream component 12 and/or on the diverging portion of downstreamcomponent 16. When openings 31 are utilized, they are preferably atleast on downstream component 16 as downstream component 16 ispreferably longer than upstream component 12, making downstreamcomponent 16 more prone to a larger stagnant flow zone.

FIG. 5 is a cross-sectional view of fluid modulator 10 with a pluralityof openings 31 that act as flashing flow channels.

FIG. 6 illustrates fluid modulator 10 where outlet 15 of upstreamcomponent 12 is positioned downstream from entry 21 of downstreamcomponent 16. In this example, distance x is negative and D1 is largerthan d1, e.g., at least 1 mm larger. As shown, outlet 15 and entry 21may both be positioned downstream past the intersection of the branchlumen(s) and the body lumen.

FIG. 7 shows a manner for selecting the diameter D1 at entry of thedownstream component 16 relative to the distance x from outlet 15 ofupstream component 12 so as to receive all the fluid jetted from outlet15. As shown, D1 is greater for larger distances x to ensure receipt ofthe fluid jetted from upstream component 12.

FIG. 8 illustrates fluid modulator 10 constructed similarly to fluidflow modulators 10 of FIGS. 2 and 3A, although gap 14 is along a portionthat extends radially outward from outlet 15 of upstream component 12.Gap 14 is formed along a curved portion (e.g., S-shaped) between fluidflow structure 18 and outlet 15. This curved portion allows downstreamcomponent 16 to be close to the branched lumen(s). In addition, fluidflow structure 18 is positioned downstream from the intersection betweenthe branched lumen(s) and the body lumen for simplicity and additionalanchoring support. Fluid modulator 10 may be formed from a common frame(e.g., a single stent design), which facilitates control of the distancex between outlet 15 and entry 21. A single structure also facilitatesco-axial orientation, especially for eccentric upstream and downstreamcomponents.

FIG. 9 illustrates flow modulator 10 constructed similarly to flowmodulator 10 of FIG. 8, although downstream component 16 includes curvedportion 32 (e.g., S-shaped) that extends radially outward to contact theinner wall of the body lumen. A second curved portion downstream indownstream component 16 provides further radially force to enhancedanchoring within the body lumen and also gives a longer diffuser for agiven length. Flow modulator 10 also may include an additional gap(s) soas to not block fluid flowing from other branched vessels, such as gap33 at the downstream end of downstream component 16.

Reference is now made to FIG. 10 and FIG. 11, which illustrate flowmodulators 10 with gap 14 positioned asymmetrically with respect toupstream component 12 and downstream component 16. In other words, gap14 is not positioned along the axis of the major vessel between upstreamcomponent 12 and downstream component 16, but instead is offset towardsone of upstream component 12 and downstream component 16.

The left side structure of FIGS. 10 and 11 may be the upstream ordownstream direction, depending on the application; thus, the left sidestructure is labeled 12 or 16 and the right side structure is labeled 16or 12.

FIG. 12 illustrates a construction of either upstream component 12 ordownstream component 16, depending on the direction of flow. Thestructure includes relatively wide portion 35 which converges intorelatively narrow portion 36. Relatively narrow portion 36 extends intodiverging portion 37 which serves as a sealing portion.

FIG. 13 illustrates another construction of either upstream component 12or downstream component 16, depending on the direction of flow. Thestructure of converging portion 38 includes surfaces that curve backwardin the opposite direction.

FIGS. 14A and 14B illustrate another construction of either upstreamcomponent 12 or downstream component 16. In this construction, firststent member 39 may be installed with converging and diverging portions(FIG. 14A) and afterwards second stent member 40 may be installed overfirst stent member 39 to define a final converging and diverging shape.FIG. 14A may also be used as is, without the additional stent member. Itis noted that the first stent member does not have to touch the secondstent member (diffuser stent) and can be shorter than that shown in thedrawings.

FIG. 15 illustrates an alternative design in which upstream component 12is constructed of a plurality of discrete objects 41, such as but notlimited to, spheres, balloons, rods, and the like, which graduallyincrease in size to create the converging effect. Similarly, downstreamcomponent 16 may be constructed of a plurality of discrete objects 41,such as but not limited to, spheres, balloons, rods, and the like, whichgradually decrease in size to create the diverging effect. Discreteobjects 41 may be optionally covered with membrane 42 to provide asmooth flow surface.

FIG. 16 illustrates flow modulator 10 of FIG. 2 installed in a bodylumen 43, such that gap 14 is situated at a bifurcation 44.

FIG. 17 illustrates another embodiment of flow modulator 10 installed inthe body lumen 43, such that gap 14 is situated at bifurcation 44. Inthis embodiment, fluid flow structure 18 includes extension 46 that isdeployed in bifurcation 44. The opening in the stent graft at the bottomof the device (in the sense of FIG. 17; of course, it could be situatedin a different location other than “bottom”), may be used instead ofsleeve-like extension 46. Alternatively, extension 46 may be used bothat the top and the bottom, or an opening may be used at the top andbottom or any other combination.

FIG. 18 illustrates the flow modulator of one of the embodimentsinstalled in the aortic arch, such that gap 14 is situated at thebifurcation of the carotid arteries. This installation may be used toreduce peak pressure gradients or to divert emboli away from the carotidarteries with very little pressure loss.

FIG. 19 illustrates a flow modulator installed near the kidneys. Forexample, upstream component 12 may be installed in the inferior venacava just below (upstream to) the branch off to the renal vein and thedownstream component 16 may be installed in the inferior vena cava justabove (downstream to) the branch off to the renal vein. Gap 14 is at thebranch to the renal vein. Flow modulator 10 creates a reduced pressureregion in the vicinity of gap 14 and increases blood flow velocity atgap 14. Entrainment may also help draw blood into the gap from thekidneys. In this manner, the invention can draw blood from the kidneysto the renal veins and then to the inferior vena cava, thereby improvingkidney functionality and reducing necrotic damage to the kidneys.

Reference is now made to FIG. 20, which illustrates another constructionof either upstream component or downstream component, depending on thedirection of flow. The structure includes outer stent 90 and inner stent92. Outer stent 90 may be cylindrical. Inner stent 92 may includerelatively wide portion 93 which converges into relatively narrowportion 94. Relatively narrow portion 94 extends into slightly divergingportion 95 with very little energy losses. The two stents may be joinedtogether (such as, but not limited to, by welding or other suitabletechnique) and at least partially coated with coating 96 (although theymay be used as bare metal, uncoated stents as well). The order of thejoining and coating processes may be joining before coating or coatingbefore joining.

Reference is now made to FIG. 21, which illustrates another version ofthe embodiment of FIG. 20. In this version, outer stent 90 is shorter sothat coating 96 coats over the end of outer stent 90.

Reference is now made to FIG. 22, which illustrates flow modulator 100,in accordance with another non-limiting embodiment of the presentinvention. Flow modulator 100 includes pump 102, such as but not limitedto, an axial flow pump, centrifugal pump, booster pump, chopper pump andmany others. Pump 102 may be secured in place by a stent or may becoupled to a portion of the upstream component 12 or downstreamcomponent 16. Pump 102 may be located either downstream or upstream,depending on the particular application. Pump 102 may be used to augmentblood flow and filtration, for example.

Any of the embodiments of the invention may serve to divert emboli orother debris, so there is no need to use an extra filtration device. Oneexample is using the upstream component or downstream component at ornear the carotid arteries to divert emboli or other debris.

Reference is now made to FIG. 23, which illustrates flow modulator 10(or any other flow modulator of the invention) installed in an aneurysm101. The flow modulator is installed through the blood vessel and lowerspressure at the aneurysm site, so as to help prevent the aneurysm fromincreasing in size or bursting, and perhaps decreasing the size of theaneurysm. The flow modulator works even without sealing against theaneurysm.

If there are one or more side branch lumens at or near the aneurysmsite, the device reduces the pressure but also permits blood to flow tothe side branches. This is in contrast to circular stent grafts of theprior art which disadvantageously block the side branches. If there areno side branches, then the device just reduces the pressure withoutincreasing the blood flow.

A filter may be optionally used with the flow modulator to preventembolic debris from flowing from the aneurysm to other blood vessels.

Reference is now made to FIG. 24, which illustrates flow modulator 110,in accordance with another non-limiting embodiment of the presentinvention. Flow modulator 110 includes upstream component 112 withoutlet 113 and downstream component 116 which has an upstream divergentmouth entry 117. Outlet 113 enters entry 117 and this area serves as gap114. Outlet 113 may be coupled with support 115 to a portion ofdownstream component 116, for example, to center outlet 113 with respectto entry 117. Alternatively, a separate stent structure (which does nothinder flow) may be used to support outlet 113.

The straight portion in downstream component 116 may help straighten theflow before it is diffused and reduce flow separation form the diffuserwall, thereby reducing pressure losses.

FIG. 24 shows one example of flow modulator 110 installed in a renalapplication. In this example, upstream component 112 may be installed inthe inferior vena cava upstream to the branch off to the renal vein andthe downstream component 116 may be installed in the inferior vena cavadownstream to the branch off to the renal vein. Outlet 113 is alsodownstream to the branch off to the renal vein. Similar to theembodiment of FIG. 19, flow modulator 110 creates reduced pressure atoutlet 113 in gap 114, which increases blood flow velocity from therenal vein to the gap.

Reference is now made to FIG. 25, which illustrates flow modulator 120,in accordance with another non-limiting embodiment of the presentinvention. Flow modulator 120 includes upstream component 122 withoutlet 123 and downstream component 126. Upstream component 122 hasfirst portion 128 which is not in-line with downstream component 126,but is instead tilted relative thereto and which may be installed in abranch lumen, as shown in FIG. 15. Outlet 123 may be directed to thecenter of the inlet to downstream component 126. Outlet 123 may becoupled with support 125 to a portion of downstream component 126, forexample, to center the nozzle with respect to the inlet. Alternatively,a separate stent structure (which does not hinder flow) may be used tosupport outlet 123.

Reference is now made to FIG. 26, which illustrates lumen support member130 installed with flow modulator 10, in accordance with anothernon-limiting embodiment of the present invention. Lumen support member130, which may be a stent body, helps support the body lumen fromcollapsing inwards during reduced pressure.

Reference is now made to FIG. 27, which illustrates that in any of theembodiments, upstream component 12 and/or downstream component 16 maynot seal against the inner contour of the body lumen, but instead may bespaced from the inner contour of the body lumen. For example, thisarrangement prevents blocking flow from a side branch 73. Although thismay create pressure losses, it still reduces pressure as compared tojust using a nozzle, and it may improve flow out of the body lumen, suchas improving flow out of a vein.

Reference is now made to FIG. 28, which illustrates that the transitionbetween upstream component 12 to downstream component 16 (the region ofgap 14) may be off-center from the center line C-C of the body lumen. Insuch an embodiment, the transition between upstream component 12 todownstream component 16 is asymmetric with respect to the center line ofthe body lumen. For example, this may be used advantageously if there isonly one side branch—the asymmetry will favor flow from the side branch;if there are two side branches, the asymmetry will favor flow from oneof the side branches.

Reference is now made to FIGS. 29A and 29B, which illustrate upstreamcomponent or downstream component 80, whose shape is changeable inaccordance with another non-limiting embodiment of the presentinvention. Upstream component and downstream component 80 may becombined to create a nozzle/diffuser configuration with a gaptherebetween similar to the structures described throughout thisdisclosure.

Accelerator or decelerator 80 may include one or more inflatablemembers, such as end faces 82 and 84 coupled by intermediate member 85,such as but not limited to, inflatable balloons or bladders, which canbe inflated or deflated by introducing or extracting fluid into or frominflatable members 82 and 84 (connected to a suitable fluid source, suchas water, saline, air, etc. Intermediate member 85 may be a covermaterial and/or may be pre-shaped (e.g., a cylindrical shape like astent) thereby creating radial force on inflatable members 82 and/or 84to create better sealing. Changing the size of inflatable members 82 and84 changes the flow characteristics through the device. For example, onecan change how much the device diverges or converges. Inflatable members82 and 84 may be connected by longitudinal members 86, which may also beinflatable and thus changeable in size, such as changeable in length orthickness.

The device may be deployed in the deflated state and then inflatedin-situ. In the example where the upstream component and the downstreamcomponent are combined into one device, the respective inflatablemembers may be inflated/deflated simultaneously with a common lumen in acatheter or individually using a multi-lumen catheter. After the patienthas reached a stable condition, the device may be deflated or inflatedas needed to adapt to changing conditions. The device may be deflatedfor removal from the body. A reservoir of fluid may be implanted withthe device for use in inflating the device after installation in thebody. The device may be held against the inner walls of the body lumenor may be separated from them, as described above for other embodiments.

As is explained above, flow modulator 10 is sized and shaped to beimplanted in a body lumen. Flow modulator 10 may be compressible fordelivery (e.g., percutaneous delivery within a delivery sheath) andexpandable upon deployment (e.g., self-expanding upon exposure from thedistal end of the delivery sheath or balloon expandable).

Referring now to FIG. 30, flow modulator 10 is shown in the compressed,delivery configuration within sheath 150 in accordance with anothernon-limiting embodiment of the present invention. Flow modulator 10 maybe coupled to transition portion 152 and/or wire 154 to facilitatedelivery to the body lumen and retrieval from the body lumen. Transitionportion 152 illustratively has a non-concentric cone shape to facilitatecompression into sheath 150 and is coupled to upstream component 12although it may be coupled to downstream component 16. Wire 154 iscoupled to transition portion.

FIGS. 31A and 31B show flow modulator 10 in the expanded, deployedconfiguration outside of sheath 150. Flow modulator 10 may transition tothe expanded, deployed configuration when exposed past the distal end ofsheath 150. For example, sheath 150 may be pulled proximally against afixed stopper in sheath 150 to unsheath flow modulator 10 at a targetlocation within a body lumen, e.g., where the renal veins intersect withthe inferior vena cava.

Flow modulator 10 may be retrieved from the body lumen (e.g., inferiorvena cava). For example, a sheath may be threaded over wire 154 and wire154 may be fixed in place (e.g., ex vivo fixation of the proximal end ofthe wire). Then, the sheath is pushed against transition portion 152 tocompress flow modulator 10 within the sheath. Flow modulator 10 and thesheath are then removed from the patient.

Referring now to FIG. 32, flow modulator 10 is shown in accordance withanother non-limiting embodiment of the present invention. Flow modulator10 is similar to flow modulator 10 of FIG. 3A, although flow modulator10 of FIG. 32 further includes retrieval mechanism 160. Retrievalmechanism 160 may be coupled to the proximal end of upstream component12 as illustrated. In this manner a retrieval device, e.g., hook 166,may be coupled to retrieval mechanism 160 to pull retrieval mechanismtowards sheath 164 to compress flow modulator 10 into sheath 164 forretrieval. For example, retrieval mechanism 160 may be configured like asnare with a plurality of arms coupled to the end of upstream component12 and coupled together near the center of the flow path within upstreamcomponent 12. Flow component 10 may be implanted with retrievalmechanism 160 coupled thereon or retrieval mechanism 160 may be coupledto flow modulator 10 during the retrieval process. Flow modulator 10 inFIG. 32 also includes retrieval mechanism 162 at an opposing end of flowmodulator, e.g., coupled to the end of downstream component 16.Retrieval mechanism 162 works in the same manner as retrieval mechanism160. Use of two retrieval mechanisms may be particularly helpful whenflow modulator 10 is formed from a braided structure since the diameterof the structure decreases as the braid is lengthened. Retrievalmechanisms 160 and/or 162 may also be used for partial retrieval. Forexample, retrieval mechanism 160 and/162 may be pulled (simultaneouslyor at different times) in a direction(s) away gap 14 to partially orfully reduce the diameter of flow modulator 10 within a body lumen. Suchreduction would allow for washing of any stagnant flow zones createdadjacent to flow modulator 10. Flow modulator 10 could then be fullyremoved, repositioned within the body lumen and expanded, or expanded inthe prior deployment location within the body lumen.

FIGS. 33A and 33B show hook 166 coupled to retrieval mechanism 160 inthe compressed state within sheath 164 and in the expanded state outsideof sheath 164.

Referring now to FIG. 34, flow modulator 10 is shown in accordance withanother non-limiting embodiment of the present invention. Flow modulator10 is similar to flow modulator 10 of FIG. 3A, although flow modulator10 of FIG. 34 further includes ring 172. In this illustration, frame 168is formed from a plurality of ribs and defines upstream component 12 anddownstream component 16. Frame 168 may be formed from a shape memorymaterial such as shape memory metal. Frame 168 is coated withbiocompatible material 170 at upstream component 12 and downstreamcomponent 16 to define the flow channels and the uncoated portion offrame 168 therebetween defines gap 14. Ring 172 is disposed around aportion of frame 168 and maintains the portion disposed therein in acompressed configuration. For example, in the deployed state down inFIG. 34, ring 172 is disposed around the portion of fluid modulatorbetween upstream component 12 and downstream component 16 to cause frame168 to form a converging cross-sectional flow area at upstream component12 and a diverging cross-sectional flow area at downstream component 16.Ring 172 is configured to move along frame 168 to transition theportions of frame 168 disposed within ring 172 from an expanded state toa contracted state. Shaft 174 may be coupled to ring 172 such thatmovement of shaft 174 moves ring 172 along frame 168.

Flow modulator 10 is deliverable in a compressed state within a sheathto a target location within a body lumen. Once suitably positioned, flowmodulator 10 is exposed from the sheath (e.g., by pulling the sheathproximally while flow modulator 10 remains in place) and flow modulator10 self-expands to the deployed configuration. Flow modulator 10 may bepartially retrieved (e.g., compressed to allow for washing) and/or fullyretrieved by moving ring 172 proximally (e.g., by pulling shaft 174proximally) to compress upstream component 12 or downstream component 16to a diameter suitable for insertion within a sheath. The remainingportion of flow modulator 10 may then be compressed within the sheathand removed from the body via the sheath.

FIG. 35 illustrates a bench test used for determining the optimalconfiguration for a flow modulator constructed in accordance with thepresent invention. In the bench test, a flow modulator was placed in amain lumen (to simulate the inferior vena cava) such that the gap waspositioned at a branch lumen (to simulate a renal vein). The bench modelutilized a constant steady flow in the main branch and was connected toan over flow bath to maintain constant physiological pressure. Water wasused for the fluid and blood analogue was used to verify the trends. Aside branch pipe with a controlled resistance was connected to a liftedreservoir (to simulate renal filtration pressure). The resistance in theside branch was fixed in a rate to create a normal renal flow with anormal net filtration pressure. As a result, fluid flow was low when thepressure gradient between the renal bath to the main lumen was smaller.

Three pressure sensors (shown as P1, P2, and P3 in FIG. 35) wereconnected to the simulated IVC (upstream to the side branch, at the sidebranch level, and downstream to side branch). A magnetic flow sensor wasused to measure IVC flow. Renal flow was measured with a digital weightscale with a computer interface via rs232. Thus, mass flow rate can bemeasured (or flow rate since the density can be calculated) withoutcreating additional pressure loss.

FIG. 36 is a graph showing the results for one representatives IVC flowrate (2 liters per minute (L/min)). The graph shows renal flow in mL/minversus pressure difference in mmHg for various configurations shown inFIGS. 37A-37E. Data points 200 are for a nozzle and diffuserconfiguration (shown in FIG. 37E) based on the flow modulator principlesdescribed herein. In this example, the upstream nozzle has an outletinner diameter of 5 mm and the downstream diffuser has an entry innerdiameter of 5.5 mm. As shown in FIG. 36, the renal flow is highest forthis configuration and the table below shows that this nozzle anddiffuser configuration create significantly less pressure loss than allother configurations. Data points 202 are for a single nozzleconfiguration (shown in FIG. 37B). The same upstream nozzle was used asthe upstream nozzle in the nozzle and diffuser configuration. As shownin FIG. 36, the renal flow is lower than the nozzle/diffuserconfiguration, but higher than the other configurations and the pressureloss of 11 mmHg shown in the table below is significantly larger thanthe pressure loss of the nozzle and diffuser configuration. Data points204 are for baseline, meaning no device is used (shown in FIG. 37A). Asshown in FIG. 36, only the nozzle and diffuser configuration based onthe principles of the present invention is significantly better thanbaseline. Data points 206 are for two nozzles in the same direction(shown in FIG. 37C). As shown in FIG. 36, renal flow is actuallynegative, which would send blood flow in the renal veins in the wrongdirection. In addition, the table below confirms the pressure loss of 22mmHg is high. The same upstream nozzle was used as above and thedownstream nozzle has an outlet inner diameter of 5 mm. Data points 208,210, and 212 are for two nozzles in opposite directions for distancesbetween the outlet of the upstream nozzle and the inlet of thedownstream nozzle of 35 mm (shown in FIG. 37D), 12 mm, and 4 mm,respectively. The same upstream nozzle was used as above and thedownstream nozzle has an inlet inner diameter of 5 mm. For data points208 where the distance is 35 mm, similar to data points 206, renal flowis actually negative, which would send blood flow in the renal veins inthe wrong direction. In addition, the table below confirms the pressureloss of 22 mmHg is high. For data points 210 and 212, the renal flow isaround or worse than baseline and the pressure loss is high at 14 mmHg.

Configuration Pressure loss [mmHg] Nozzle and diffuser  5 Nozzle 11 2Nozzle same direction 22 2 Nozzle opposite direction distance −35 mm 222 Nozzle opposite direction distance −12 mm 14 2 Nozzle oppositedirection distance −4 mm 14

Thus, Applicant has discovered that using a maximum distance between theoutlet of the upstream component and the entry to the downstreamcomponent will improve flow rates in the branched vessel(s) withrelatively low pressure loss. A distance too great will create asignificant pressure loss that actually sends flow in the wrongdirection in the renal vein(s). In addition, other structuralcharacteristics of the downstream component improve renal flow with lowpressure loss such as a greater inner diameter at the entry of thedownstream component than the inner diameter at the outlet of theupstream component, a greater length of the diverging area of thedownstream component than the length of the converging area of theupstream component, and/or a lesser average angle of divergence of thedownstream component than the average angle of convergence of theupstream component.

While preferred illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. The appended claims are intended to cover all such changesand modifications that fall within the true spirit and scope of theinvention.

What is claimed is:
 1. An implantable device for altering fluid flowthrough a body lumen, the body lumen coupled to a branch lumen, theimplantable device comprising: a flow modulator configured to beimplanted within the body lumen, the flow modulator comprising anupstream component separated by a gap from a downstream component, theupstream component having an inlet, an outlet, and a cross-sectionalflow area that converges from the inlet towards the outlet, thedownstream component having an entry, an exit, and a cross-sectionalflow area that diverges from the entry towards the exit, the outlet ofthe upstream component being a distance less than 15 mm from the entryof the downstream component, wherein the gap defines a pathway thatcommunicates with the branch lumen, wherein the flow modulator isconfigured to accelerate a fluid stream passing through the upstreamcomponent towards the downstream component to generate a low pressureregion in the vicinity of the gap and to entrain additional fluid intothe fluid stream as the fluid stream passes into the entry of thedownstream component.
 2. The implantable device of claim 1, wherein thecross-sectional flow area at the outlet of the upstream component isless than the cross-sectional flow area at the entry of the downstreamcomponent.
 3. The implantable device of claim 1, wherein the outlet ofthe upstream component is positioned downstream from where the branchlumen first intersects with the body lumen.
 4. The implantable device ofclaim 1, wherein the gap begins downstream from where the branch lumenfirst intersects with the body lumen.
 5. The implantable device of claim1, wherein the upstream component and the downstream component share acommon, collinear flow axis with the body lumen's flow axis.
 6. Theimplantable device of claim 1, wherein the outlet of the upstreamcomponent is positioned downstream from the entry of the downstreamcomponent.
 7. The implantable device of claim 1, wherein the upstreamcomponent is coupled to the downstream component via a fluid flowstructure that defines the gap, wherein the upstream component, thedownstream component, and the fluid flow structure are formed from asingle frame.
 8. The implantable device of claim 7, wherein the fluidflow structure extends outward from the upstream component and from thedownstream component such that the fluid flow structure contacts aninner wall of the body lumen.
 9. The implantable device of claim 7,wherein a junction between the fluid flow structure and at least one ofthe upstream component or the downstream component has an S-curve shape.10. The implantable device of claim 1, wherein the downstreamcomponent's length is greater than the upstream component's length. 11.The implantable device of claim 1, wherein the upstream component'saverage angle of convergence is greater than the downstream component'saverage angle of divergence.
 12. The implantable device of claim 1,wherein the upstream component comprises a nozzle that accelerates thefluid stream passing through the upstream component and the downstreamcomponent comprises a diffuser that decelerates the fluid stream havingthe entrained additional fluid passing through the downstream component.13. An implantable device for altering fluid flow through a body lumen,the body lumen coupled to a branch lumen, the implantable devicecomprising: a flow modulator configured to be implanted within the bodylumen, the flow modulator comprising an upstream component separated bya gap from a downstream component, the upstream component having aninlet, an outlet, and a cross-sectional flow area that converges fromthe inlet towards the outlet, the downstream component having an entry,an exit, and a cross-sectional flow area that diverges from the entrytowards the exit, the cross-sectional flow area at the outlet being lessthan the cross-sectional flow area at the entry, wherein the gap definesa pathway that communicates with the branch lumen, wherein the flowmodulator is configured to accelerate a fluid stream passing through theupstream component towards the downstream component to generate a lowpressure region in the vicinity of the gap and to entrain additionalfluid into the fluid stream as the fluid stream passes into the entry ofthe downstream component.
 14. The implantable device of claim 13, theoutlet of the upstream component is positioned downstream from where thebranch lumen first intersects with the body lumen.
 15. The implantabledevice of claim 13, wherein the gap begins downstream from where thebranch lumen first intersects with the body lumen.
 16. The implantabledevice of claim 13, wherein the outlet of the upstream component ispositioned downstream from the entry of the downstream component. 17.The implantable device of claim 13, wherein the upstream component iscoupled to the downstream component via a fluid flow structure thatdefines the gap.
 18. The implantable device of claim 13, wherein theflow modulator is formed from a metal frame.
 19. The implantable deviceof claim 18, wherein the metal frame is coated with a biocompatiblematerial at the upstream component and at the downstream component. 20.A method for altering fluid flow through a body lumen, the body lumencoupled to a branch lumen, the method comprising: implanting a flowmodulator within a body lumen, the flow modulator comprising an upstreamcomponent separated by a gap from a downstream component, the upstreamcomponent being implanted in a first body lumen portion and having aninlet, an outlet, and a cross-sectional flow area that converges fromthe inlet towards the outlet, the downstream component being implantedin a second body lumen portion and having an entry, an exit, and across-sectional flow area that diverges from the entry towards the exit,and the gap being positioned where the branch lumen intersects with thebody lumen and the outlet being positioned downstream from where thebranch lumen first intersects with the body lumen; and accelerating afluid stream passing through the upstream component towards thedownstream component to generate a low pressure region in the vicinityof the gap and to entrain additional fluid into the fluid stream as thefluid stream passes into the entry of the downstream component.
 21. Themethod of claim 20, wherein implanting the flow modulator within thebody lumen comprises implanting the upstream component in an inferiorvena cava such that the inlet is upstream from a branch off to a renalvein and the downstream component in the inferior vena cava such thatthe exit is downstream from the branch off to the renal vein, whereinthe gap is at the branch to the renal vein, thereby drawing blood to therenal vein and improving kidney functionality.
 22. The method of claim21, wherein drawing the blood to the renal vein to improve kidneyfunctionality further reduces excess fluid to treat heart failure. 23.The method of claim 20, wherein the flow modulator modulates fluid flowwithout any input from an external energy source.
 24. The method ofclaim 20, wherein the flow modulator modulates fluid flow without anymoving parts.